Synthetic rubber



United States Patent 3,14,780 SYNTHETIC RUBBER Wilbur J. Wald, Bellevue, Pa., assignor to Neville Chemical Company, Pittsburgh, Pa, a corporation of Pennsylvania N0 Drawing. Filed Mar. 4, 1966, Ser. No. 12,701

11 Claims. (Cl. Mill-$3.6)

This invention relates to improved compounds and methods for producing improved compounded elastomeric compositions based on oil-extended diene homopolymers of, for example, butadiene, isoprene, chloroprene, etc., and copolymers of these with styrene and its homologues.

Of late years the use of certain hydrocarbon oils in the higher than previously used molecular weight SBR polymers has produced an advantageous raw material for the rubber industry. The introduction of the cold (41 F. polymerized) SBR with its higher molecular weight and greater abrasion resistance was in itself an advance of recognized importance in the development .of the industry. The development of latex blending and subsequent coagulation of the cold SBR latex and emulsified extender-oils was an equally important [advance in that it extended existing plan-t capacity at little or no added cost, produced a product of lower vulcanized hardness and modulus, while at the same time the effect on ultimate tensile strength was slight. The method lowered the cost of the compounded rubber appreciably. The good abrasion resistance, lower heat build-up and quieter and smoother ride found in tire operation as a result of the lower compounded hardness were further plus values.

As the degree of oil extension increased from 25 through 37.5 to 50 phr. (parts per hundred of rubber hydrocarbon) problems of splice and ply adhesion, both green and cured, and of oil bleeding or migration into the natural rubber tire cushion and natural rubber coated tire cords resulted in somewhat more rapid deterioration of the natural rubber compound. As a consequence there was a tendency toward weakening and separation of the plies in the tire with ultimate premature tire failure.

Such bleeding tendencies show even to a greater extent in those rubber compounds containing mineral and other fillers having relatively low oil absorbing. properties, and in those compounds which have been cured or vulcanized to a higher degree than usual. Heat aging of any compound based on oil-extended SBR will intensify whatever bleeding tendencies it may have. For the production of commercial products of safe utilization and reliable quality at an economical level, this bleeding tendency must be controlled. If the bleeding can be controlled, and at the same time the final cost of the rubber product further lowered the full advantages of these modern developments can be realized.

The present invention is based on the discovery that far superior compound stability from the point of view of bleeding or migration of oil, or oil and other components, can be imparted to the compound through the addition of certain relatively low molecular weight hydrocarbon resins. At the same time the addition of such resins aid in the dispersion of the fillers, pigments and reinforcing agents during the rubber compounding step particularly when a Banbury, rubber mill, or other mechanical means is used, and further aids in bringing out the maximum idhififid Patented July 13, 1965 iCe physical properties to be obtained from a given loading of filler.

As will be shown later, not all hydrocarbon resins of the same relatively low molecular weight will accomplish this result. In fact, the addition of some has been found to intensify the undesirable bleeding tendencies at a given proportion of oil to rubber hydrocarbons. Proper selection of the resin used can also aid in adjusting the hardness of the final compound to some degree.

As the amount of suitable resin is increased in a rubber compound the oil bleeding tendency becomes less and [any plasticizing action in excess of that desired can often be used to an economic advantage by further increasing proportions of filler and other components. For some compounds it may be found desirable to use as high as or more parts of resin per hundred of rubber. This, of course, would be accompanied by a corresponding adjustment in curing agents, increase in filler loading, and resulting llower compound cost. Such high resin loadings may also encourage further oil-extension of the present high molecular weight butadiene-styrene copolymers, as well as the development and use of even higher molecular weight butadiene-styrene copolymers, without encountering -or aggrevating bleeding difliculties. It was not so long ago that the use of even 25 phr. of pla-sticizing (extending) oil in a tire compound would have been judged fantastic. Now 50 phr. of oil-extension in SBR polymer is being introduced commercially. The use of these resins make further oil-extension, even above the present 50 phr., practical.

Resin loadings of 100 and even higher parts per hundred parts of high oil-extended butadiene-styrene el astomer would be the most practical in mechanical goods such as floor mats, floor tile, stair treads, etc., where the advantage of increased amounts of hardening filler can be used at an appreciable economic savings.

In the following text the butadiene-styrene copolymer elastomers are used as a readily recognizable example. This invention can also apply to other high molecular weight synthetic diene rubbers such as those of butadiene, isoprene, and homologues alone or copolymerized with for example styrene :or its homologues by any of the polymerization methods known to the art that will yield a polymer capable of exhibiting elastomeric properties alone or in combination with such extending oils, said polymers having the characteristics hereinafter set forth.

At present the most common butadiene-styrene copolymer elastomer is that comm-only known as GR-S or SBR and is prepared from about three parts of butadiene and one part of styrene by Weight. The present invention is applicable to any butadiene-styrene ratio which produces a high molecular weight elastomer which may be extended by the addition of large proportions of extending-oil whether such oil be of naphthenic, aromatic, or mixed hydrocarbon nature.

In the process of the present invention the resin may be mixed into the already prepared oil-extended el-astomer by any practical mechanical means such as the Banbury, rubber mill, or mixing ex-truder, .eg., the so-called Plasticator. On the other hand the resin may be dispersed in water by any :of the methods known .to the art and then blended with the elastomer latex [along with the desired extending-oil in emulsion form, prior to coagulation by the usual methods. By another method, the extendingoil and resin may first be blended, preferably with some heating to'speed the operation; the blend dispersed in water; and this water dispersion blended with the elastomer latex prior to coagulation.

One of the last two, i.e., the latex-dispersion blending processes, is to be preferred over mechanicatlmethods for reasons; of optimum dispersion, greater product uniformity, and lower cost of operation. Moreover, these are the only practical methods of compounding the higher molecular weight SBR eilastomers which tend to tear or disintegrate in mechanical mills.

If desired, water dispersionsof carbon black, clays, antioxidants, or other desired materials may be blended into the elastomer-res-in-oil-water dispersed blend prior to coagulation Without interfering with the purpose of this invention. It is contemplated that such commonly used rubber components may be used in the amounts and'for the purposes for which they are intended.

After coagulation and drying by any method acceptable in the art, these socalled latex master-batches or water dispersion blends may be further dry compounded on a rubber mill, in a Banbury, or by other mechanical mixer, as desired.

In a broad embodiment, the invention comprises a method (and the resulting composition) .for inhibiting or preventing bleeding of oil or oil and other ingredients, from oil miasterbatch high molecular weight elast omeric polymers with which the invention is concerned, for example, styrene-butadiene el'astomer-ic copolymers. The oil masterbatch comprises polymers having Mooney viscosities (raw) in excess of about 60 (ML. 100 C./4'), and hydrocarbon oils, for example, petroleum oils, at least about 90% of which boil above 250 C., the oil being present in the proportions of at least about 35 phr. (parts per hundred parts of rubber hydrocarbon), said masterbatch in the cured or uncured state being subject to bleeding of oil or oil and other components. In the oil masterbatch is included .a synthetic thermoplastic resin selected from the group consisting of coumarone-indene accentuated by high portions orparaflinic side, chains.

and polyindene res'ins, .ball and ring softening point about 10 C. to about 125 C. (up to about 18 phr).

The composition may contain the usual additives employed in compounded rubbers. These will vary depending in part upon the end use and in part upon the character of the elastomer, the extender oil, and the resin employed. These include fillers, pigments, vulcanizing or curing agents, accelerators, antioxidants, etc., etc.

The elastomer may be made by known methods for producing the high molecular weight elastomers with which this invention is concerned. The usual method for producing the higher molecular weight SBR at present involves low temperature (e.g., 41 F.) catalytic copolymerization of butadiene and styrene in the ratios of approxi mately 2:1 to 3:1, although this process is applicable to a wider range of monomer ratios, say from 100% diene to 2:1 diene to styrene. The method of making the elastomer is not a part of this invention.

The oilsused in the oil masterbatch are those which are currently used or have been proposed for use in the high oil-extended, high molecular-weight SBR polymers which have a tendency to bleed or migrate from the, polymer paticularly when used in proportions of 50 phr. or higher. The tendency to bleed becomes greater as larger proportions of oil are used, 'or as the specific gravity, or the viscosity-gravity constant of the oil decreases. The

extender oils usually have viscosity-gravity constants above about 0.79.

The tendency to bleed under oil extension alone constitutes a limiting factor on molecular weight of elastomers which can be used at present. Because of bleeding some of the tougher elastomers generally cannot be used and full advantages of these elastomers cannot be realized.

The present invention is designed to overcome this problem.

Since the range of the present oils the paraffinic compounds are in general waxy, little paraffinic compounds,

This is further emphasized it the naphth enic rings are increased over the aromaticfrings present in the oil.

Although oils of higher portions of 'paraflinic side chains, and. low portions of aromatic rings show less compatibility by their tendencyto bleed from'a rubber compound, and are more difii-cult to incorporate into the polymer; they do offer better low temperature flexibility and lighter color.

On the other hand the highly aromatic oils, although more expensive when highly refined, are more compatible bleed less and process more easilypbut introduce less low temperature ilexibility'and darker'color and/or a tendency to darken with time. The greater softening tend.- enc-l-es and hence the proportion of oil and associated economic savings is limited,'since the savings are directly related to the proportion of oil used.

Consequently, for light colored compounds, and for low temperature applications it is desirable to select an oil with a minimum of aromatic content required for compatibility or non-bleeding results, and as much 'parafiinic side-chain structure as possible Through the use of the resins proposed, the oils with more parafiinic side'chains along with naphthenic rings and less aromatic rings can be used successfully. Also a higher loadingof the otherwise bleeding oil can be used in the presenceof one of these resins. I

Those oils tending toward the more aromatic side which can to a great extent be used alone in some proportions without bleeding, can be favorably assisted in compound stability and hardness at higher levels of oil extension through the addition of an appropriate quantity of one or more of these resins. The invention also permits use of proportions of aromatic oils which would result in bleeding if used alone- The exact portions will of course depend on the particular rubber compound and its proposed application.

Extender oils of particular utility are largely composed of naphthenic and alkylated naphthenic hydrocarbons and mixtures of these with some aromatic hydrocarbons.

These may be obtained .from high boiling fractions of the so-called naphthenic or mixed base crude oils such as Midcontinent, Louisiana, East Texas, etc., crude oils.

They may .comprisedistillate fractions boiling above about v200? C. Suitable fractions are those at least of which boil above about 250 C.. More volatile members may be lost during or after compounding and curing the rubber. The oil shouldbe free of waxes and asphaltenes for most purposes. It may comprise the rafiinate from solvent extraction of topped or reduced crude oils or other high boiling, straight-run petroleum fractions, for

example, distillates, the 10% and 90% points ofwhich lie in the range of about 250 C..to, 400?- C. The solvents may be (propane and cresylic acids), sulfur dioxide, furfnral and others. Wax, if present, may be removed or its proportions reduced-by methodswell known in the petroleum industry. Under some conditions the presence of limited amounts of paraffin wax maynot be objectionable and even maybe desirable for ozone protecwith both normal and high molecular weight SBR for the purpose of increasing the bulk of the rubber and reducing its cost. Up until recently the principal use has been in normal SBR rubbers, having Mooney viscosities of about 50 or below and the proportions of oil has been of the order of 25 phr. or less.

These oils are not considered in the rubber softening or plasticizing sense of World War II synthetic rubber compounding days when to 20 phr. was generally considered high. Rather they are used at much higher levels and for different purposes. Loadings of 37.5 phr. of oils have been used for some time. Currently levels of 50 phr. of oil are being introduced commercially. Even higher loadings are possible. The following statement in Ind. & Eng. Chem., 45, 1053 (May, 1953) may give some idea of the earlier purposes, and meaning of extender-oils.

The oil extended products utilize a high Mooney viscosity cold GR-S to which is added a cheap petroleum oil in quantities sufficient to soften the rubber to extend it so that the final viscosity of the extended stock is within the usable range which (i.e., the extended rubber) is treated in subsequent processing, compounding and curing operations as if it were 100% rubber hydrocarbon.

In general, plasticizers or softeners used in compounding straight GR-S, as for example, GR-S 1006 (a nonstaining, hot polymerized butadienestyrene copolymer rubber containing a nominal bound styrene content of 23.5%) would be used at a much lower level, possibly at 5 to 10 phr., than the more modern extender-oil in oil-extended SBR of more recent development. The principal reason for this is the difference in molecular weight of the base polymer as indicated by Mooney viscosity, dilute solution viscosity, or ease of processing. GRS 1006 can be readily processed, i.e., milled or banded, on standard commercial rubber equipment, without the need for any plasticizer or softener.

This is not true in the case of the much higher molecular weight low temperature (41 F.) polymerized SBR polymers used for preparing the oil-extended synthetic rubbers such as Pliofiex 1713 or 1714c (general purpose, cold polymerized butadient-styrene copolymer rubbers containing a nominal bound styrene content of 23.5% and extended with 50 parts per hundred of a naphthenic oil and of a highly aromatic oil, respectively). An attempt to mill such a polymer without oil-extension would result in tearing and crumbling of the polymer. Such a polymer would have to be degraded in molecular weight to somewhere near the molecular weight of GR-S 1006 before it could be banded on the mill. This would destroy the advantages in properties, in production volume per unit of equipment, and in economies that the higher molecular weight polymer combined with oil-extension offers.

We propose to stabilize and extend these higher molecular weight polymer-extender-oil blends through the addition of specific types of hydrocarbon resins, i.e., cumarone-indene resins having a ring and ball softening point in the range between about 10 C. and 125 C. This three-way combination allows the use: 1) of a wider range of extender-oils in that the border lines of oil bleeding from the polymer-oil mixture are expanded to include otherwise less compatible extender-oils by decreasing the tendency of the polymer-extender-oil-resin mixture to separate; (2) of yet higher molecular weight, much tougher (higher Mooney viscosity) base polymers than practical at present oil-extended levels, i.e., 50 phr. of extender-oil, through the use of these more stable polymer-oil-resin combinations; and (3) of greater volume extension of current base polymers recently introduced in the 50 phr. oil-extended commercial products through the use of 50 or more phr. of extender-oil plus various amounts of stabilizing and further extending resin.

All of these decrease the cost of the final product which can be considered as the total rubber hydrocarbon content in compounding and increase the volume and weight of the rubber produced by existing equipment.

Obviously, the higher the molecular weight of the base polymer, as judged by increased viscosity, the greater the amount of extender-oil required to bring it down to the commercially processible range.

The introduction of one of our hydrocarbon resins in addition to the oil will permit an increase in the amount of oil that can be added before bleeding occurs. If one of the resins having a softening point appreciably above room temperature is used, less softening eifect will be found at a given oil level, or more oil can be added to produce the desired softness. At the same time the total rubber volume or weight is thus further extended by the amount of resin used. Such a system applied to still higher molecular weight base polymers allows even further extension with oil and resin, with the accompanying overall greater savings in costs. In any case the presence of the resin produces a more stable system.

The following are examples illustrating the invention. The rubber base compound was prepared using Pliofiex 1713XF, a non-staining, non-discoloring, cold SBR rubber extended with 50 phr. of a naphthenic type oil having a viscosity-gravity constant of about 0.803 and refractivity intercept of 1.045.

The 10% boiling point of the oil was 270 C. and the point 393 C. (ASTM D850). It had a specific gravity of about 0.874, a Gardner color of 8+, and an aniline point of C. The refractive index at 20 C. was 1.4818. The unsulfonated residue in fuming sulfuric acid (20% S0 was less than 1% by volume.

BASE COMPOUND Parts/wt.

Plioflex 1713X-F 100 Stearic acid 2 Zinc oxide 3 AgeRite HP 1 1 1 A blend of about 65 parts phenyl-beta-naphthy1amine and about 35 parts of diphenyl-pphenylenediamine.

Philblack O (a high abrasion furnace black) 50 Sulfur 2 Amax 1.25

2 N-oxydiethylene benzothiazo1e-2 su1fenamide.

Altax 0.25

3 Benzothiazyl disulfide.

Resin 0, 5, 10, or 20 These components were mixed on a rubber mill and then press cured at 310 F. for 20 minutes. The compound containing no resin was, of course, the control. The resins used at the 5, 10, or 20 parts per hundred of rubber hydrocarbon were:

(1) A. coumarone-indene resin, B. & R. softening point, 104 C., produced by conventional catalytic polymerization of a coal tar naphtha fraction boiling between about C. and about 200 C.

(2) A hydrocarbon resin obtained by catalytic reaction of a mixture of monomers composed essentially of linear dienes and reactive olefins, having an average molecular weight of about 90, to produce a hard solid resin with a. resulting average molecular weight approximating 1100 and about 100 C. B. 8: R. softening point. This resin appears to be methylated parafiin chains containing only a limited amount of unsaturation.

These resins gave the results shown in Table I in (A) the oil-extended rubber with resin alone, and (B) in the cured compound. The cured, unaged compound was tested by contact with a cigarette paper under 2 p.s.i. pressure at room temperature. The cured and aged compound was tested by finger contact.

a, 1 as, re o 7' 8 Table I. Oil staining Resin No. 1, phr. Resin No. 2, phr; Control (A) Medium Stain .Stain Stain Stain 1. Strong stain.-- Strong stain No test. (B) I Unaged:

Dei Def Def Strong Strong Strong. (B) II Aged: Slight; N one Some More Very much. Extrcme Extreme.

1 phr.=Parts per hundred of rubber. a

1 Oven aged 2 weeks at 70 C. The aged samples were inspected for surface oil by finger contact instead of weighted cigarette paper.

(A) =Unvulcanized oil-extended rubber plus resin.

(B) =Vulcanized rubber compound.

Dei.=Definite stain, percent of area of test paper stained.

These tests showed that compounds containing Resnl Part B No. 2 showed bleeding of an oily material on the surface under :all conditions tested and very soon after mixing. It has actually been shown that Resin No. 2 creates or very greatly intensifies oil bleeding characteristics where little or none originally appeared. Consequently, that type of resin is not useful in such compounds.

Compounds containing Resin N0. 1 were eifective in retaining the extender-oil at the lower resin content levels but showed surface bleeding at the higher resin levels. This'indieates that Resin No. 1 will furnish some practical advantages in oil-extended rubber compounds up to about 18 phr.

In those cases where hardness is desired with less filler loading at a given resin content, Resin No. 1 may be pre- 'ferred.

In view of their lower oil adsorbing properties, compounds containing mineral fillers may enjoy an increased advantage in bleeding control through the use of these resins. Tighter cures without bleeding can also be used in the presence of these resins.

Mixing 0r masterbatching.lt has been shown that the above resins can be blended into the butadiene-styrene elastomer either by iechanical mixing by any known method of the dry oil-extended polymer with the resin; or by dispersing the resin in water and blending the resin dispersion along with the extending-oil emulsion into the butadiene-styrene elastorner latex as it comes from the polymerizers; or by hot-melt blending of the extendingoil and resin prior to dispersing the combination in water and subsequently blending the extending-oil-resin dispersion with the butadiene-styrene elastorner latex as it comes from the polymerizer and prior to coagulation and drying.

The latex mixing systems are much to be preferred because of the shorter time required, the more intimate mixtures obtained, the greater product uniformity, and the appreciably lower cost of the latex mixing operation over the high power consumption and high costmachinery required for mechanical blending. Further, the latex lending procedure Will result in much less degradation of the higher molecular weight butadiene-styrene copolyrners. The importance of preventing the copolymer degradation under mechanical mastication increases as the molecular weight of the butadiene-styrene eopolymer selected increases.

The following are examples of the dispersions used in latex blending.

DISPERSION NO. 1

Parts by wt. Resin 100 Sodium soap of acintol D 5 Distilled Water 145 Dispersed at room temperature.

DISPERSION NO. 2.IN SlTU METHOD Part A Parts by wt. Resin 100 Actinol D 4.38

I 7 Parts by Weight Sodium hydroxide 0.62 Distilled water 145;00

*Acintol D is a product composed of tall oil acids in the rattilo of 30% rosin acids and 70% high molecular weight fatty an s. a

Part A is hot-melt blended, cooled and ground before dispersing in Part B with strong agitation at room temperature.

DISPERSION NO. 3

'Parts by wt. Resin Distilled water 57.4 Darvan No. 1* 2.4 Bentonite 0.25

Darvan No. 1 is a product composed of polymerized sodium salts of alkylnaphthalene sulfonic acids. The components were ground together at room temperature. V

DISPERSION NO. 4'.-HOT-MELT Distilled water 163.9

Part A was hot-melt blended together, cooled to to C., and added to Part B at ,65 to 75 C. with good agitation. V

DISPERSION NO. 5.HOT-MELT PartA Parts by wt. Resin 90.0 Extending-oil 150.0 Actinol D 10.5

I PartB. Sodium hydroxide 1.5 'Distilled water 228.0

Mixed as in Dispersion No. 4.

The first three examples of dispersions were charged to the butadiene-styrene copol ymer latex after the antioxidant dispersion and the extending-oil emulsion had been stirred in as separate operations. The ratios used were those required to give 50 phr. extending-oil and either 5, 10, or 20 phr. of resin as desired in the final coagulate. I

In the case of Dispersions-4 and 5, which were the dispersions of hot-melt blends of 15 to 60 parts of the resin per parts of'the extending oil, the ratios of extending-oil'to resin were preset and the combined dispersion was charged to the required amount ofbutadienestyrene latex for 50 phr. oil-extension following the addition of the antioxidant dispersion. e

I claim:

1. In the manufacture of improved, non-bleeding vulcanizates from an oil master-batch high molecular weight elastomeric diene polymer, said oil masterbatch comprising a polymer having a Mooney viscosity in excess of about 60 (ML. 100 C./4), and containing at least 35 parts per 100 parts of elastomer of a hydrocarbon extender oil at least about 90% of which boils above 250 C., the said oil and the proportion thereof in the masterbatch being such that a :bleeding vulcanizate is obtained upon curing in the absence of added resin; the improvement which comprises incorporating in said oil masterbatch, prior to curing, about 5 parts (per 100 parts of polymer) of a thermoplastic coumarone-indene resin having a ball and ring softening point from about C. to about 125 C.

2. A cured rubbery composition comprising an oil masterbatch high molecular weight elastomeric polymer, said oil masterbatch comprising a polymer having a Mooney viscosity in excess of 60 (ML. 100 C./4'), at least about 35 parts (per 100 parts of polymer) of a hydrocarbon extender oil composed predominantly of naphthenic and alkylated naphthenic hydrocarbons, at least about 90% by volume of which extender oil boils above about 250 C., and about 5 parts (per 100 parts of poly-.

mer) of a synthetic thermoplastic coumarone-indene resin having a ball and ring softening point from about 10 C. to about 125 C.

3. The method of claim 1 wherein the elastomer is a styrene-butadiene copolymer.

4. The method of claim 1 wherein the elastomer is polyisoprene.

5. The method of claim 1 wherein the elastomer is polychloroprene.

6. The method of claim 1 wherein the elastomer is polybutadiene.

7. The composition of claim 2 wherein the elatsomer is a styrene-butadiene copolymer.

8. The composition of claim 2 wherein the elastomer is polyisoprene.

9. The composition of claim 2 wherein the elastorner is polybutadiene.

10. A process for making improved oil-extended rubber from a latex of an elastomeric copolymer of butadiene and styrene, which process comprises making a blend by hot melting a coumarone-indene resin having a ball and ring softening point from about 10 to about 125 C. and a hydrocarbon extender oil at least 90% of which boils above 250 C. and which is composed pre dominantly of naphthenic and alkylated naphthenic hydrocarbons, in a proportion of about 15 to parts of the resin per 100 parts of the oil, dispersing said blend in water at a temperature between about and C., adding the resulting dispersion to the latex of the elastomeric copolymer in a proportion to provide about 35 to about 50 parts of said extender oil and about 5 parts of the coumarone-indene resin per parts of said copolymer, and coagulating, compounding and curing the resulting mixture.

11. A process according to claim 10 wherein tall oil acids are included in said resin-oil blend and sodium hydroxide is included in the water in which said blend is tobe dispersed, whereby said acids and sodium hydroxide form a soap when said blend is dispersed in the water.

References Cited by the Examiner UNITED STATES PATENTS 2,421,627 6/47 La Crosse 26045.5 2,427,942 9/47 Bulifant 260-45.5 2,875,170 2/59 Ayers et al. 260-336 2,964,083 12/60 Pfau et al. 26033.6 2,993,023 7/61 Pfau et al. 260--33.6

OTHER REFERENCES Earley et al., Mechanical Properties of High Mooney Elastomers, Rubber Age, April 1954, pages 65-72.

Whitby et al., Synthetic Rubber, Wiley & Sons, New York, page 410.

MORRIS LIEBMAN, Primary Examiner.

DANIEL ARNOLD, LEON J. BERCOVITZ,

Examiners. 

1. IN THE MANUFACTURE OF IMPROVED, NON-BLEEDING VULCANIZATES FROM AN OIL MASTERBATCH HIGH MOLECULAR WEIGHT ELASTOMERIC DIENE POLYMER, SAID OIL MASTERBATCH COMPRISING A POLYMER HAVING A MOONEY VISCOSITY IN EXCESS OF ABOUT 60 (M.L. 100*C./4''), AND CONTAINING AT LEAST 35 PARTS PER 100 PARTS OF ELASTOMER OF A HYDROCARBON EXTENDER OIL AT LEAST ABOUT 90% OF WHICH BOILS ABOVE 250*C., THE SAID OIL AND THE PROPORTION THEREOF IN THE MASTERBATCH BEING SUCH THAT A BLEEDING VULCANIZATE IS OBTAINED UPON CURING IN THE ABSENCE OF ADDED RESIN; THE IMPROVEMENT WHICH COMPRISES INCORPORATING IN SAID OIL MASTERBATCH, PRIOR TO CURING, ABOUT 5 PARTS (PER 100 PARTS OF POLYMER) OF A THERMOSPLASTIC COUMARONE-INDENE RESIN HAVING A BALL AND RING SOFTENING POINT FROM ABOUT 10*C. TO ABOUT 125*C. 